# Piezoeletricity

Pierre and Jacques Curie initially discovered the piezoelectric effect in 1880. The two scientists observed that when pressure was exerted on a small piece of quartz, it produced an electric potential. It was later found that when an electric potential was applied (via an electric field) to the same material, there was also a change in length. Thus, the name piezoelectricity (Greek for pressure electricity) was given to this anomaly. .
Piezoelectricity can be used in many different applications. The first application of piezoelectricity came around in 1917, when Langevin used quartz transducers to generate and detect underwater acoustic waves. This invention was eventually used for submarine detection. One of the most important applications of piezoelectricity was radio communications. First described by Nicholson in 1919, the application was finally put into use by WEAF in New York when they put up the first quartz crystal controlled transmitter in 1926. Piezoelectricity can be defined as the generation of static charge due to the creation of a dipole moment. A quick illustration can be done using a model of a tetrahedron in an electric field: .
Using symmetry, one finds that the net dipole moment is zero at equilibrium. However, a dipole moment becomes present when the molecule is stretched or compressed in a perpendicular or parallel direction along one of the vertices. This effect can be done mechanically (e.g. Hitting the material with a hammer), or using an electric field. In an electric field, charged atoms stretch/compress due to their attraction or repulsion in the electric field (as shown in Figure 1), giving rise to the change in dipole moment. Piezoelectric materials are ranked using their piezoelectric coefficients. The piezoelectric coefficients (listed as "a" and "b" in the equation below) are constants that relate to the polarization and strain due to the material exposed to an electric field: P = aF; S = bE Where P is defined as the pressure exerted on the material, 'a' is the piezoelectric pressure coefficient.

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